The present invention claims priority from Japanese Patent Application 2002-140438 filed in Japan on May 15, 2002. The content of this Japanese application is hereby incorporated in the specification of the present application by reference.
1. Field of the Invention
This invention relates to a valve driving device of an internal combustion engine, and in particular to a device which performs opening and closing of a valve system using fluid pressure, without having a cam mechanism.
2. Description of the Related Art
So-called camless valve driving devices, which eliminate cams for valve driving and instead employ electromagnetic driving or hydraulic driving of the valve in order to enhance freedom of engine control, are viewed as promising. Such technology is disclosed in Japanese Patent Publication No. 7-62442 and in Japanese Patent No. 2645482, wherein the valve opening and closing timing and lift amount of the device can be set freely.
In such a device, high fluid pressure is developed sufficient to lift the valve by the necessary amount in opposition to the valve spring, and this pressure is applied to the valve to perform the desired lifting. However, a large amount of energy is required for valve driving to simply apply high fluid pressure to the valve, the valve driving loss is increased, and there is the disadvantage that a decrease in fuel efficiency may result.
In order to resolve this problem, the inventors newly invented a valve driving device of an internal combustion engine which utilizes low-pressure fluid to greatly reduce the valve driving energy. In this device, a pressure chamber to which is supplied actuating fluid to open the valve is connected to three passages, which are a passage to supply high-pressure actuating fluid, a passage to introduce low-pressure actuating fluid, and a passage to discharge actuating fluid from the pressure chamber; valves are provided in each passage.
However, in this structure the volume of the pressure chamber is necessarily large, and energy must be supplied through high-pressure actuating fluid to the pressure chamber when performing driving to open the valve. Hence the fraction of available energy which is the fraction of conversion into kinetic valve energy relative to the energy supplied during the valve opening is reduced, the valve driving energy is increased, and worsened output and fuel efficiency may result.
The present invention was devised in light of the above problems, and has as an object the provision of a valve driving device of an internal combustion engine in which the volume of the pressure chamber is reduced insofar as possible and the energy supplied during driving to open the valve is decreased, while at the same time the available energy fraction is increased, valve driving energy is reduced, and output and fuel efficiency are raised.
This invention is a valve driving mechanism to drive the opening and closing of a main valve serving as an intake valve or as an exhaust valve of an internal combustion engine, and comprises a pressure chamber, to which is supplied pressurized actuating fluid to open the above main valve; a high-pressure actuating fluid supply source, connected to the above pressure chamber; a low-pressure actuating fluid supply source, connected to the above pressure chamber; a first actuating valve, provided between the above pressure chamber and the above high-pressure actuating fluid supply source, which is opened for a prescribed period in the initial opening period of the above main valve, and which supplies high-pressure actuating fluid from the above high-pressure actuating fluid supply source to the above pressure chamber; a second actuating valve, comprising a check-valve provided between the above pressure chamber and the above low-pressure actuating fluid supply source, which, after the prescribed interval in the initial opening period of the above main valve has elapsed, is opened when the pressure of the above pressure chamber is lower than the pressure of the above low-pressure actuating fluid supply source based on the pressure difference therebetween, to introduce low-pressure actuating fluid from the above low-pressure actuating fluid supply source into the above pressure chamber; a third actuating valve comprising a check-valve, provided either between the above second actuating valve and the above low-pressure actuating fluid supply source or in the above low-pressure actuating fluid supply source, which is opened when the intake-side pressure becomes higher than the pressure of the above low-pressure actuating fluid supply source and also higher than a prescribed pressure setting which is lower than the pressure of the above high-pressure actuating fluid supply source, and by this means discharges actuating fluid from the above pressure chamber; and, an actuator which forcibly opens the above second actuating valve during opening of the above main valve.
It is preferable that the above third actuating valve be provided between the above second actuating valve and the above low-pressure actuating fluid supply source, that the second actuating valve and third actuating valve be comprised by a single valve unit, and that the above low-pressure actuating fluid supply source be connected to the above valve unit.
It is also preferable that the above second actuating valve comprises a valve body movable in the axis direction, that poppet valve portion which receives the pressure on the side of the above pressure chamber and is impelled to the closed-valve side is provided at one end of this valve body, and that the above actuator comprise an electrical actuator which when turned on impels the other end of the above valve body to drive the above valve body to the open-valve side.
It is also preferable that a valve stopper be provided to set a maximum opening for the above second actuating valve.
In a preferred aspect of this invention, when the main valve is opened (lifted), the first actuating valve is open and high-pressure actuating fluid is supplied to the pressure chamber. By this means initial energy is provided to the main valve, and thereafter the valve is lifted by inertial motion. In this process, when the pressure of the pressure chamber falls below the pressure of the low-pressure actuating fluid supply source, the second actuating valve opens independently, and low-pressure actuating fluid is introduced into the pressure chamber. By this means a large amount of actuating fluid is supplied to the pressure chamber, exceeding the amount of high-pressure actuating fluid supplied, so that there is never negative pressure in the pressure chamber, the main valve can be held in the valve lifted position reached by the above-described initial energy, and the driving energy used during main valve lifting can be reduced.
When the main valve is closed, the second actuating valve is forcibly opened by the actuator. Then, after the high-pressure actuating fluid in the pressure chamber passes through the second actuating valve, the third actuating valve on the downstream side is pushed open, and the high-pressure actuating fluid is discharged to the outside. By this means the pressure in the pressure chamber falls and the main valve is closed.